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2.2 L61 Code P0420 - 2004 Cavalier

Ok new issue....

Last week I threw a CEL that started flashing when I drove the car. P0300 random multiple cylinder misfire. I replaced the Ignition Control Module and cleared the code. Car ran fine.

Same day about 25 miles later I threw another CEL. This time I pulled P0420 Catalyst Effeciency Below Threshold Bank 1. I cleared the code, drove it for about 95 miles and 3 days, just got the light again so I'm assuming it's the same thing.

I've been searching and reading... O2 sensors or a bad cat is what I've come to gather. The car's only got 43k on it and this just started happening after the ICM went out so I'm not gonna start throwing money at it until I find out where the problem really lies. I want to test the O2 sensors before replacing, but I'm not sure how. Would a normal voltmeter read it? Where do I physically test them at?

What other options do I have? I just find it hard to swallow that if your ICM acts up then it starts other problems... I only drove it a half mile back to my house with it running bad.

Throw me a frickin' bone here?

PS. My inspection is due today 1/31... These things always seem to happen at the best of times right?

What state are you getting it inspected in, depending on how they do their test if they just plug in a obdII reader they are going to get a not ready code when you get it inspected. If they put a sniffer in the tailpipe you might be ok. Do you have a high flow cat or is your exhaust stock? There is a cheap fix involving 2 spark plug anti foulers being plugged into your rear o2 sensor bung and then screwing the sensor into the anti foulers that will get rid of your code. I had the same code as you for a long time and did this trick and has been off for about 7 months now.

I'd rather fix it then get the anti-foulers, but if that comes down to it then I will... Just would like to know what's making it happen.

I live in Pennsylvania, and I think they just use a sniffer. I'm going to pull my spark plugs (Bosch Platinum +2) which seem to be the issue from my ICM and maybe even this, then get a new O2 eventually.

Allegheny here too. If its under warranty go for the new cat, if not the cheapest fix is going to be the spark plug anti foulers like I mentioned. Kind of weird for it to throw this code if your using the stock cat, did you have any exhaust work done to your car?

Well I sucked it up and took it to the stealership. Paid the diag fee and it's a cat fault...

However, they won't replace the cat under federal 8/80 warranty because my car is an R title (for a nonsense reason too). So it looks like I'll be strapping a universal cat on there to get it inspected.

Well I sucked it up and took it to the stealership. Paid the diag fee and it's a cat fault...

However, they won't replace the cat under federal 8/80 warranty because my car is an R title (for a nonsense reason too). So it looks like I'll be strapping a universal cat on there to get it inspected.